I. Field of the Invention
The present invention relates generally to communications, and more specifically, to enhancing the scheduling of data transmissions.
II. Background
The field of wireless communications has many applications including, e.g., cordless telephones, paging, wireless local loops, personal digital assistants (PDAs), Internet telephony, and satellite communication systems. A particularly important application is cellular telephone systems for mobile subscribers. (As used herein, the term xe2x80x9ccellularxe2x80x9d encompasses both cellular and personal communications services (PCS) frequencies.) Various over-the-air interfaces have been developed for such cellular telephone systems including, e.g., frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). In connection therewith, various domestic and international standards have been established including, e.g., Advanced Mobile Phone Service (AMPS), Global System for Mobile (GSM), and Interim Standard 95 (IS-95). In particular, IS-95 and its derivatives, IS-95A, IS-95B, ANSI J-STD-008 (often referred to collectively herein as IS-95), and proposed high-data-rate systems for data, etc. are promulgated by the Telecommunication Industry Association (TIA), the International Telecommunications Union (ITU), and other well known standards bodies.
Cellular telephone systems configured in accordance with the use of the IS-95 standard employ CDMA signal processing techniques to provide highly efficient and robust cellular telephone service. Exemplary cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. Pat. Nos. 5,103,459 and 4,901,307, which are assigned to the assignee of the present invention and fully incorporated herein by reference. An exemplary described system utilizing CDMA techniques is the cdma2000 ITU-R Radio Transmission Technology (RTT) Candidate Submission (referred to herein as cdma2000), issued by the TIA. The standard for cdma2000 is given in draft versions of IS-2000 and has been approved by the TIA. The cdma2000 proposal is backwards compatible with IS-95 systems. Another CDMA standard is the W-CDMA standard, as embodied in 3rd Generation Partnership Project xe2x80x9c3GPPxe2x80x9d, Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214.
In the CDMA systems introduced above, voice and data traffic can be carried in message frames of various lengths. Typically, a remote station in the range of a base station must receive and decode a plurality of message frames in order to determine the complete voice and data payload information. Preambles are attached to the message frames to convey information as to the number of message frames that will carry a given payload. In addition to the number of frames that are needed to carry the full payload, preambles can also carry information identifying the target destinations and the transmission rates of the message frames. Other information, such as the radio link protocol (RLP) sequence numbers of the message frames, can also be included. Hence, the accurate decoding of message frames is dependent upon the detection and decoding of the preambles attached to said message frames.
It is desirable to use knowledge of the successful or unsuccessful decoding of preambles and associated message frames to optimize the throughput of the system. In particular, it would be desirable to use such information to quickly alter the transmission schedules of message frames.
An ARQ channel is implemented on the reverse link of a communication system, wherein an acknowledgment or negative acknowledgment is transmitted in response to a received transmission. A system is herein presented for changing an already existing transmission schedule based on signals or lack of signals on the ARQ channel.
In one aspect, a method for enhancing a transmission schedule is presented. The method includes transmitting a plurality of preamble subpackets and a plurality of data traffic subpackets in parallel in accordance with the transmission schedule; monitoring for a signal on an acknowledgment channel; if a signal is not detected, continuing to transmit in accordance with the transmission schedule; if a signal is detected, determining whether the sender of the signal is a targeted station; if the signal is from the targeted station, then canceling the transmission schedule and forming a new transmission schedule with new data traffic if the signal is an acknowledgment, or sending a retransmission in accordance with the transmission schedule if the signal is a negative acknowledgment; and if the signal is not from the targeted station, then suspending a retransmission for a time period less than or equal to one second if the signal is negative acknowledgment or transmitting a retransmission if the signal is an acknowledgment.
In another aspect, an apparatus in a base station for adjusting an existing scheduling scheme for transmitting redundant data packets is presented. The apparatus includes a preamble channel generator for transmitting preamble subpackets; a data traffic channel generator for transmitting data traffic subpackets; a scheduling element electrically coupled to the preamble channel generator and the data traffic channel generator, the scheduling element for controlling the packing of preamble information into the preamble subpackets and data traffic into the data traffic subpackets, and for controlling the transmission sequence of the preamble subpackets and the transmission sequence of the data traffic subpackets; and a receiver subsystem electrically coupled to the scheduling element, the receiver subsystem for detecting a signal received on an acknowledgment channel from a remote station, wherein the scheduling element controls the transmission sequence of the preamble subpackets and the transmission sequence of the data traffic subpackets in accordance with the signal or lack thereof on the acknowledgment channel, wherein the arrival of the signal indicates that the preamble subpacket was successfully decoded and the non-arrival of the signal indicates that the preamble subpacket was not successfully decoded.